The document discusses four main theories of language acquisition:
1) Imitation theory proposes that language is learned through imitation, repetition, and reinforcement of utterances.
2) Nativist or innateness theory argues that humans are born with an innate language acquisition device that allows them to learn language quickly based on innate linguistic principles and parameters.
3) Cognition theory views language acquisition through a cognitive-psychological lens, focusing on mental processes like reasoning.
4) Motherese or input theory emphasizes the role of maternal input and interactions in aiding language development.